Thermal transfer ribbons generally comprise a backing film, one surface of which is coated with at least one hot-melt ink layer, the opposite surface being most commonly covered with a protection layer called a back.
Conventionally, thermal transfer printing consists in depositing, when the ribbon passes under a print head, by means of the heat provided by heating points (called “resistances” or “dots”) of the print head of the printer, the hot-melt ink in the form, for example, of various characters (date, code, number, logo, etc.), on a recipient substrate (paper, cardboard, synthetic film, etc.). The ink of the thermal transfer ribbon is transformed (by fluidification or sublimation) under the effect of the heat, and by simple pressure is transferred in the form of characters onto said recipient substrate.
In order to allow optimum writing quality, in particular according to the speed and temperature constraints exerted by the printer, it is necessary for the back of the ribbon to be able to dissipate the high energy (temperature) supplied by the print head and to withstand the phenomenon of friction and abrasion between said head and the ribbon.
At the current time, ribbons for thermal transfer printing generally consist of three main parts, namely:                a backing film of small thickness which is conventionally made of a polymer, for example of polyamide or polyester type, such as polyethylene terephthalate (PET), which is in particular bi-oriented;        one surface of this film is coated with an inked system, i.e. with at least one layer of ink which is hot-meltable for the purpose of being transferred during printing onto a recipient substrate, optionally combined with an adhesion layer and/or a protection layer for said ink layer;        the other surface of the film is coated with at least one layer called a back intended to protect said film, while at the same time promoting the slip under the print heads.        
This very long ink ribbon is rolled up on itself on mandrels. It must be uniform over its entire length and width.
The presence of a “back” protective layer is essential when the backing film is thin. This is because the ribbon must withstand the various mechanical stresses (elongation, traction) in both dimensions.
Moreover, this back must allow thermal conductivity through its thickness in order to transmit the energy, supplied by the print head, to the inked system present on the opposite surface of the film.
Other protective layers can thus be integrated into the thermal transfer ribbon, in particular on the surface bearing the inked system:                a protective layer can be deposited directly on the backing film and then be covered with the layer of hot-melt ink, such a layer making it possible to protect the ink once printed on the recipient substrate;        a protective layer can also be deposited on the external surface of the ink layer of the ribbon, this layer making it possible to protect the ribbon, during its storage, against its environment (this is because in particular moisture and high temperatures can cause degradation of the ink layer).        